Vibronic mode

In summary, all the transitions expected for the neutral states of a model system for conjugated polymers, the m-LPPP, were observed and described and all of these transitions also show clearly resolved vibronic replicas due to coupling to vibronic modes of the backbone. 

An effective Hamiltonian for a static cooperative Jahn-Teller effect acting in the space of intra-site active vibronic modes is derived on a microscopic basis, including the interaction with phonon and uniform strains. The developed approach allows for simple treatment of cooperative Jahn-Teller distortions and orbital ordering in crystals, especially with strong vibronic interaction on sites. It also allows to describe quantitatively the induced distortions of non-Jahn-Teller type. 

This method was used to fit the experimental results shown in Figure 3.38, except that the multichannel WR(r) was substituted for the single-channel one because the highly exergonic recombination excites the vibronic mode (whose frequency go = 43.5 x 10 3 eV and corresponding reorganization energy 0.61 eV were taken from Ref. 187). IET fits well the experimental data at a reasonable L= 1.38 A and other parameters [98] and reinforces the fact of principal importance the very existence of the maximum in Z(D) dependence. 

As described previously, nonradiative decay due to solvent interactions can severely reduce lanthanide luminescence through energy dissipation by vibronic modes, with the O—H oscillator being the most common and eflBcient quencher. However, if these O—H oscillators are replaced with lower-frequency O—D oscillators, the eflBciency of vibronic deactivation decreases substantially. Therefore, the rate constants for luminescence lifetimes (th o) of lanthanide excited states in water or alcoholic solvents are often much shorter than those in analogous deuterated solvents (td o)- This property can be utilized to determine the degree of solvation for luminescent lanthanides. 

Abstract Contribution of the Jahn-Teller system to the elastic moduli and ultrasonic wave attenuation of the diluted crystals is discussed in the frames of phenomenological approach and on the basis of quantum-mechanical theory. Both, resonant and relaxation processes are considered. The procedure of distinguishing the nature of the anomalies (either resonant or relaxation) in the elastic moduli and attenuation of ultrasound as well as generalized method for reconstruction of the relaxation time temperature dependence are described in detail. Particular attention is paid to the physical parameters of the Jahn-Teller complex that could be determined using the ultrasonic technique, namely, the potential barrier, the type of the vibronic modes and their frequency, the tunnelling splitting, the deformation potential and the energy of inevitable strain. The experimental results obtained in some zinc-blende crystals doped with 3d ions are presented. 

Because the energy state of a Jahn-Teller complex depends on the local lattice distortions, the macroscopic long-distant strain that produces an ultrasonic wave should influence it as well. The cross effect is initiated by the Jahn-Teller complexes (1) the dispersion (i.e., frequency-dependent variation of phase velocity) and (2) attenuation of the wave. In terms of the elastic moduli it sounds as appearance (or account) of the Jahn-Teller contribution to the real and imaginary parts of the elastic moduli. For a small-amplitude wave it is a summand Ac. Obviously, interaction between the Jahn-Teller system and the ultrasonic wave takes place only if the wave, while its propagation in a crystal, produces the lattice distortions corresponding to one of the vibronic modes. 

Interaction of the impurity with the e vibronic mode was considered [12] and, therefore, the local distortions have tetragonal type. The adiabatic potential in this case has three minima and the energy in the minima was introduced in the following form... 

Table 1 Potential barriers Fq, softening moduli, active vibronic modes, and vibrational frequencies determined in ultrasonic experiments carried out on the zinc-blende crystals doped with "id ions...

A previous report has demonstrated how the temperature dependence of the piezomodulation spectra has been able to produce a more detailed picture of the interaction of the side chains with the polymer spine (23). It was shown that different vibronic modes became active at different temperatures for a uniaxial stress along the b-axis of the crystal. 

Using the strategy for optimal pump-dump control based on the intermediate target, we have shown that the isomerization pathway through the conical intersection can be suppressed and that optimized pulses can drive the isomerization process to the desired objective (isomer 11). This means that the complex systems are amenable to control, provided that the intermediate target exists. Furthermore, the analysis of the MD and of the tailored pulses allows for the identification of the mechanism responsible for the selection of appropriate vibronic modes necessary for the optimal control. 

At room temperature, the vibrational spectroscopy data are still contradictory about a number and nature of the transformations above 20 GPa. A sequence of new phases has been reported on the basis of several splitting of the Raman vibron modes [24], including one just above 20 GPa [27]. In contrast, x-ray studies indicate the stability of 8 phase to 50 GPa [26, 33] in agreement with latter Raman study [34]. A change in x-ray diffraction pattern was observed above 60 GPa [36], but interpretation requires additional measurements. Recent Raman and IR measurements to 42 GPa show clear correspondence between the number of observed lattice and vibron modes and group-theoretical predictions for the 8 phase [9]. 

At pressures above 90 GPa and room temperature a new Raman vibron band (V2a) become visible (see also, Ref. [35]). At this point the infrared absorption spectra of vibron modes also show a change more IR modes become visible and the overall intensity increases (Fig. 7). Phase transition has been suggested in Ref [24] on the basis of similar observations, but it was not confirmed in more recent publication [35]. The data presented here and also the results of the recent unpublished x-ray study (Sanloup et al., unpublished) clearly indicate a phase transformation at 100-110 GPa. This transition may be related to a next (probably ultimate) stage of orientation ordering of N2 molecules. 

The pressure dependence of the Raman-active vibron modes (Figs. 11(a) and 11(b)) was studied on unloading at 300 K in new phases. 1-N2 exhibits typical behavior for such molecular crystals branching of vibrational modes and increasing of separation between them with pressure due to increasing intermolecular interactions. All of the vibrational modes originate from the same center, which is close to the frequency of the V2 disk-like molecules in E-N2. Thus, the structure of the i phase is characterized by the presence of just one type of site symmetry for the molecules and the large number of vibrational modes arises from a unit... 

Fig. 11. (a) Raman (open circles) and infrared (open squares) frequencies of vibron modes as a function of pressure for i phase, (b) Raman (open circles) and in ared (open square) frequencies of 9 phase. All measurements were done on the pressure release at 309 K. Filled circles correspond to the vibron frequencies after the transformation to the 8 phase from 0 and i phases. Gray dashed lines are data for the 8 and phases from Ref. 35. 

The experimental data shown in Fig. 5 consist of IR absorption spectra of bulk PPY between two potassium bromide plates and infrared reflection absorption spectra (IRAS) of thin spin coated layers of PPY on gold. The reason for using a metal substrate in the latter case is that a well-defined reflection at a metal surface results in excitation of vibronic modes perpendicular to the plane of the film. Note that the wide band at 1200 cm-1 in the bulk spectra originates from the solvent [1]. 

Relatively weak vibronic modes are evident in the tails which broaden the bands. Even when these are eorrected, however, the best fit is unequivocally Lorentzian. The inadequaey of the spectrophotometer to give eorrect contours at the tops of the peaks and between the two major peaks becomes evident in the resolutions. 

The existence of vibronic transitions in rare earth crystals shows that the rare earth ions are coupled to the vibronic modes of the lattice we shall also show that such coupling plays a dominant role in the energy transfer process between rare earth ions in glasses. We believe that this treatment of phonon-assisted energy transfer can be extended to biologically active organic molecules such as DNA, ATP, DTP and similar molecules. 

IR and Raman vibronic modes. Resonance Raman scattering... 

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